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gogofmt

go generate with gofmt, replacing variable value

The release of the 'generate' tool opens up a whole lot of exciting possibilities. I've been trying to make my tests better. I have a function which queries an external API, the location of that API is defined in a global variable. One piece of the puzzle is replacing that value with a value determined at 'generate time'.

I have:

//go:generate gofmt -w -r "var apiUrl = a -> var apiUrl = \"http://example.com\"" $GOFILE

Running go generate then errors out with:

parsing pattern var apiUrl = a  at 1:1: expected operand, found 'var'

It's not an option to use a place holder like so:

gofmt -r 'API_GOES_HERE -> "http://example.com"' -w

That's because, when I compile production code, the source gets rewritten, so subsequent compiles for testing no longer can replace the place holder (it has been replaced already).

I realise I'm abusing gofmt somewhat but I'd rather not go back to sed. What would be the valid go:generate statement?

Solution

  • You can use a linker flag -X for that. For example,

    go build -ldflags "-X main.APIURL 'http://example.com'"

    will build your program with APIURL variable set to http://example.com.

    More info in the linker docs.

    Go 1.5 edit: starting with Go 1.5, it's recommended to use the new format:

    go build -ldflags "-X main.APIURL=http://example.com"

    (Note the equals sign.)